只能返回，不能分配，自我? [英] Can only return, not assign, Self?

问题描述

考虑此模式

extension UIViewController
{
    class func make(sb: String, id: String) -> Self
    {
        return helper(sb:sb, id:id)
    }

    private class func helper<T>(sb: String,id: String) -> T
    {
        let s = UIStoryboard(name: storyboardName, bundle: nil)
        let c = s.instantiateViewControllerWithIdentifier(id) as! T
        return c
    }
}

效果很好，所以

let s = SomeViewControllerClass.make( ... )

实际上，

返回子类"SomeViewControllerClass". (不仅仅是UIViewController.)

does in fact return the subclass "SomeViewControllerClass". (Not just a UIViewController.)

没关系，

在make中说您要进行一些设置:

say in make you want to do some setup:

    class func make(sb: String, id: String) -> Self
    {
        let h = helper(sb:sb, id:id)
        // some setup, m.view = blah etc
        return h
    }

实际上看来您无法做到这一点.

你只能

        return helper(sb:sb, id:id)

你不能

        let h = helper(sb:sb, id:id)
        return h

有解决方案吗?

推荐答案

当然有解决方案.这正是helper函数的作用.

Of course there is a solution. That's exactly what the helper function is doing.

为什么不将代码放入helper?

要调用helper这是一种通用类型，您必须以某种方式指定该类型，例如

To invoke helper, which is a generic type, you have to specify the type somehow, e.g.

let h: Self = helper(...)

或

let h = helper(...) as Self

，但是这些表达式都不实际接受Self.因此，您需要根据返回值-> Self推断类型.这就是return是唯一起作用的原因.

but neither of those expressions would actually accept Self. Therefore, you need to infer the type from the return value -> Self. That's why return is the only thing that works.

还请注意，您可以使用 second 辅助功能.

Also note that you can use a second helper function.

class func make(sb: String, id: String) -> Self {
    let instance = helper2(sb: sb, id: id)        
    return instance
}

class func helper2(sb: String, id: String) -> Self {
    return helper(sb:sb, id:id)
}

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